Superscalar processors achieve higher performance by executing multiple instructions concurrently and out-of-order. That is, instructions can be (and often are) processed out of the order that the instructions were placed into an execution pipeline. Notwithstanding contemporary out-of-order processing, conventional processors hold instructions (including completed instructions) in the execution pipeline and retire the instructions serially from the oldest instruction in the pipeline. This practice is wasteful of resources since all resources used by an instruction are held until the instruction is retired.